1. Technical Field
The present invention generally relates to a lubricating oil additive and lubricating oil composition containing same.
2. Description of the Related Art
There is increasing evidence that certain synthetic and natural chemicals may act as agonists or antagonists to estrogens or androgens and may interfere in multiple ways with the action of thyroid hormones. These chemicals can be called endocrine disruptors. For example, endocrine disruptors can (1) mimic or block chemicals naturally found in the body thereby altering the body's ability to produce hormones, (2) interfere with the way hormones travel through the body, and (3) alter the concentration of hormones reaching hormone receptors.
Endocrine disruptors and natural estrogens share a common mechanism of action. In normal cases, estrogenic activity is produced by binding natural estrogen to an estrogen receptor (ER) within the nucleus of the cell, followed by transcriptional activation of these occupied ERs. When endocrine disruptors are present, normal estrogenic activity is supplanted when endocrine disruptors bind an ER, causing transcriptional activation of the ER even though no natural estrogen is present. Similarly, antiestrogenic activity is produced by endocrine disruptors which bind to ERs, but which do not subsequently activate the occupied ER as well as natural estrogen. Finally, selective estrogen receptor modulators (SERMs) bind to ERs, but subsequently activate cellular responses that differ from those activated by the natural estrogens. In general, all but a very small number of molecules that bind to ERs produce some activation of the receptors, as either estrogens or as SERMs.
Alkylphenols and products produced from them have come under increased scrutiny due to their association as potential endocrine disruptive chemicals. This is due to the weak estrogenic activity of base alkylphenol as well as degradation intermediates of the alkylphenol products. Alkylphenols are commercially used in, for example, herbicides, gasoline additives, dyestuffs, polymer additives, surfactants, lubricating oil additives and antioxidants. In recent years, alkylphenol alkoxylates, such as ethoxylated nonylphenol, have been criticized for having poor biodegradability, high aquatic toxicity of the by-products of the biodegradation of the phenol portion. Thus, there is an increasing concern that these chemicals may act as endocrine disrupters. Some studies have shown there to be a link between alkylphenols and declining sperm count in human males and there is evidence that alkylphenols may harmfully disrupt the activity of human estrogen and androgen receptors. Specifically, Routledge et al., “Structural features of alkylphenolic chemicals associated with estrogenic activity”, J Biol. Chem., 1997 Feb. 7; 272(6):3280-8, compared different alkylphenols estrogenic activity in an estrogen-inducible strain of yeast comparing the assays with 17β-estradiol. The results indicated that optimal estrogenic activity requires a single branched alkyl group composed of between 6 and 8 carbon atoms located at the para position on an otherwise unhindered phenol ring with 4-tert-octylphenol (8 carbons also named 4-(1,1,3,3-Tetramethyl-butyl)-phenol)) having the highest activity. Routledge et al. tested various alkylphenols in the assay and indicated that alkyl chain length, degree of branching, location on the ring, and degree of isomeric heterogeneity affect the binding efficiency but was not able to draw a structure activity conclusion. For example, Routledge et al. stated that the p-nonylphenol as determined by high resolution gas chromatographic analysis identified 22 para-isomers speculating that all isomers would not have similar activity without elucidating the active species. Interestingly, Tabria et al., “Structural requirements of para-alkylphenols to bind to estrogen receptor”, Eur. J. Biochem. 262, 240-245 (1999) found that when using human estrogen receptors, the receptor binding of alkylphenols was maximized when the number of alkyl carbons was nine carbon atoms. Tabria et al. noted that branched chain nonylphenol, mixture of isomers (commercially available and which did not contain any n-nonylphenol) was almost as active as n-nonylphenol.
Nonylphenol ethoxylate and octylphenol ethoxylate are widely used as nonionic surfactants. Concern over the environmental and health impact of these alkoxylated alkylphenols has led to governmental restriction on the use of these surfactants in Europe, as well as voluntary industrial restrictions in the United States. Many industries have attempted to replace these preferred alkoxylated alkylphenol surfactants with alkoxylated linear and branched alkyl primary and secondary alcohols, but have encountered problems with odor, performance, formulating, and increased costs. Although the predominate focus has been on the alkylphenol ethoxylates and the potential problems associated with these compounds (primarily with the degradation by-products), there remains a need to review other components to select combinations that have similar or improved performance benefits with reduced negative impacts.
Nonylphenol and dodecylphenol can be produced by the following steps: propylene oligomerization and separation of propylene trimer and tetramer, and phenol alkylation with propylene trimer and separation of nonylphenol, or phenol alkylation with propylene tetramer and separation of dodecylphenol. Tetrapropenyl phenol prepared from propylene tetramer has been widely used in the lubricant additive industry. A tetramer is a highly branched chain of 10 to 15 carbons with a high degree of methyl branching that imparts oil solubility and compatibility with other oil soluble lubricant additive components. A tetramer is also a cost effective olefin to manufacture. Dodecylphenol derived from propylene tetramer is primarily used as an intermediate in the production of additives for lubricating oils, commonly sulfurized alkyl phenate detergents. To a lesser degree, these branched phenate detergents have employed some degree of linear olefin.
U.S. Patent Application Publication No. 20070049508 (“the '508 application”) discloses a lubricating oil composition containing (a) an oil of lubricating viscosity, and (b) a detergent containing an unsulfurized alkali or alkaline earth metal salt of a reaction product of (i) an olefin having at least 10 carbon atoms, wherein greater than 80 mole % of the olefin is a linear C20 to C30 n-alpha olefin, wherein less than 10 mole % of the olefin is a linear olefin of less than 20 carbon atoms, and wherein less than 5 mole % of the olefin is branched chain olefin of 18 carbons or less, and (2) a hydroxyaromatic compound. Comparative Example C in the '508 application discloses a branched pentadecylphenol calcium salt prepared by alkylating a phenol with a branched chain C14 to C18 olefin derived primarily from propylene pentamer. However, the '508 application discloses that the branched pentadecylphenol calcium salt of Comparative Example C was ineffective in preventing endocrine disruption effects.
U.S. Pat. No. 5,510,043 (“the '043 patent”) discloses a lubricating oil additive containing (a) an alkaline earth metal salt of a sulfurized monoalkylcatechol derivative and (b) a sulfurized monoalkylcatechol. The '043 patent further discloses that the sulfurized monoalkylcatechol can be obtained by sulfurizing an alkylation product of a catechol produced by reacting a catechol with an olefin such as a propylene pentamer in the presence of a catalyst. There is no disclosure in the '043 patent of endocrine disruption effects.
It is desirable to develop improved lubricating oil additives for use in lubricating oil compositions that do not exhibit endocrine disruption effects.